The present invention generally relates to an internal combustion engine for use in a motor vehicle and the like, having a self-idling governor which is capable of automatically controlling the engine speed at an idling operating condition of the engine to a target speed and more particularly, to an ignition timing control of the engine at the idling operating condition thereof.
A known internal combustion engine having a self-idling governor is disclosed in the Japanese Laid-open Patent Publication No. 54-76723 wherein a control valve is provided in a by-pass passage which communicates the upstream side and the downstream side of an intake passage by by-passing a throttle valve, with the control valve having the purpose of opening and shutting the by-pass passage and when the engine is in idling operating condition, an idling speed of the engine is controlled to become the target speed through the control of the amount of by-pass air by controlling the opening and shutting of the control valve.
Meanwhile, with respect to the ignition control of the engine, when the engine is in idling operating condition, the ignition timing thereof is usually fixed to an idling ignition timing in advance. This idling ignition timing is set to the spark delaying side in consideration of instability in combustion condition of the engine during idling operating condition thereof.
Upon continuation of engine loading condition during a certain period, immediately after the engine has been shafted to the idling operating condition from the speed decreasing condition, the engine is in relatively favorable combustion condition, since fuel injected into the combustion chamber is in favorable vaporized or atomized condition owing to the fact that the wall surface of the combustion chamber is high in temperature or the like.
Accordingly, immediately after the engine has been shifted to such an idling operating condition as described above, if the ignition timing is fixed to the idling ignition timing, it is delayed more than necessary with respect to the combustion condition of the engine and this results in that the engine is lowered in its speed. Therefore, in the above described engine having a self-idling governor, the self-idling governor is operated so as to raise the idling speed of the engine and the fuel is consumed more than necessary, with the increase of the amount of intake air.